Copying of documents has been performed since the first recording of information in document form. Documents are produced using many procedures on many types of substrates and incorporate many forms of information. Unauthorized copying of documents has also been occurring since the storage of information in document form first began. For much of the history of information documentation, the procedures used to copy original documents have been sufficiently cumbersome and costly to provide a significant impediment to unauthorized copying, thus limiting unauthorized copying to original documents of high value. However, in more recent times the introduction of new technologies for generating reproductions of original documents, has decreased the cost and inconvenience of copying documents, thus increasing the need for an effective method of inhibiting unauthorized copying of a broader range of restricted documents.
The inability of convenient, low-cost copying technologies to copy original documents containing color or continuous tone pictorial information, restricted unauthorized copying primarily to black-and-white documents containing textual information and line art. Recently, the introduction of cost effective document scanning and digital methods of signal processing and document reproduction have extended the ability to produce low cost copies of original documents to documents containing color and high quality pictorial information. It is now possible to produce copies of any type of document quickly, conveniently, and cost effectively which are indistinguishable from the original. Accordingly, the problem of unauthorized copying of original documents has been extended from simple black-and-white text to color documents, documents containing pictorial images, and photographic images. In particular, restricting the unauthorized duplication of photographic images produced by professional photographers on digital copying devices has recently become of great interest.
U.S. Pat. Nos. 5,193,853 and 5,018,767 by Wicker, disclose methods for restricting the unauthorized copying of original documents on devices utilizing opto-electronic scanning by incorporating spatially regular lines into the original document. The spacing of the lineations incorporated in the original document are carefully selected to produce Moire patterns of low spatial frequency in the reproduced document allowing it to be easily distinguished from the original and degrading the usefulness of the reproduction. Although the Moire patterns produced in the reproduced document are readily apparent to an observer, the required line pattern incorporated in the original document to produce the Moire pattern upon copying is also apparent to an observer under normal conditions of use. Additionally, production of the Moire pattern in the reproduced document requires that specific scanning pitches be employed by the copying device. Accordingly, this method of restricting unauthorized document copying is applicable only to documents such as currency or identification cards where the required line pattern can be incorporated without decreasing the usefulness of the document. Application of this technique to high quality documents is unacceptable due to the degradation of quality of the original document.
U.S. Pat. No. 5,444,779 by Daniele, discloses a method of preventing unauthorized copying by the printing of a two-dimensional encoded symbol in the original document. Upon scanning of the original document in an initial step of a copying process, the encoded symbol is detected in the digital representation of the original document and the copying process is either inhibited or allowed following billing of associated royalty fees. U.S. patent application Ser. No. 08/593,772, filed Sep. 28, 1995, by Schildkraut et al., and titled "Copy Protection System," discloses the incorporation of a symbol of a defined shape and color into a document followed by detection of the symbol in a scanned representation of the document produced by the copying device. In both disclosures, the incorporated symbol is detectable by an observer under normal conditions of use and readily defeated by cropping the symbol from the original document prior to copying. In addition, incorporation of the symbol into the document is required in the generation of the original document leading to undesired inconvenience and additional cost. Accordingly, these methods of imparting restriction from unauthorized copying are unacceptable.
U.S. Pat. No. 5,390,003 by Yamaguchi, et al.; U.S. Pat. No. 5,379,093 by Hashimoto, et al.; and U.S. Pat. No. 5,231,663 by Earl, et al.; disclose methods of recognizing a copy restricted document by the scanning and analysis of some portion of the original document and comparison of the signal obtained with the signals stored in the copying device. When the signal of a copy restricted document is recognized, the copying process is inhibited. This method of restricting unauthorized copying of documents is limited because the signals of all documents to be copy restricted must be stored in or accessible by each copying device of interest. Because the number of potential documents to be copy restricted is extremely large and always increasing, it is impractical to maintain an updated signal database in the copying devices of interest.
Methods of encrypting a digital signal into a document produced by digital means have been disclosed. These methods introduce a signal which can be detected in a copying system utilizing document scanning and signal processing. These methods offer the advantage of not being detectable by an observer under normal conditions of use, thus maintaining the usefulness of high quality copy restricted documents. However, implementation of these methods is dependent on digital production of original documents. Although increasing, production of high quality documents using digital means is still limited. Accordingly, this approach is not useful for restricting the unauthorized copying of high quality documents produced using non-digital production methods.
U.S. Pat. No. 5,412,718 by Narasimhalu, et al. discloses the use of a key associated with the physical properties of the document substrate which is required to decode the encrypted document. This method of restricting the unauthorized copying of documents is unacceptable for applications of interest to the present invention because it requires encryption of the original document rendering it useless prior to decoding.
U.S. application Ser. No. 08/598,778, filed Feb. 08, 1996, now U.S. Pat. No. 5,752,152, by John Gasper, et al., and titled, "Copy Restrictive System", and U.S. patent application Ser. No. 08/598,785, filed on Feb. 08, 1996, now U.S. Pat. No. 5,919,730, by John Gasper, et al., and titled, "Copy Restrictive Documents" disclose pre-exposing color photographic paper to spots of blue light to produce an array of yellow microdots after chemical processing and a method of detecting these microdots during scanning performed by a digital printing device. Color photographic paper capable of forming yellow microdots after exposure to spots of blue light is of the color-negative type.
Finally, U.S. patent application Ser. No. 08/837,931, filed Apr. 11, 1997, now U.S. Pat. No. 5,864,742, titled, "Copy Restrictive System For Color-Reversal Documents" by John Gasper, et al.; and U.S. patent application Ser. No. 08/835,976, filed on Apr. 11, 1997, now U.S. Pat. No. 5,772,250, titled "Copy Restrictive Color-Reversal Documents," by John Gasper, disclose pre-exposing color-reversal photographic paper to spots of blue light to produce an array of minus-yellow microdots after chemical processing and a method of detecting these microdots during scanning performed by a digital printing device. These methods prevent copying restricted documents, but are not foolproof because of operational conditions in the field.
Two components necessary to prevent a user from copying a copy restricted document are a scanner recognizable pattern of microdots on the paper or photograph which are invisible to the human eye, and a software algorithm which locates the pattern in a digital image. The software is preprogrammed to use a specific portion of the scanned region as an input. After processing, the algorithm will determine whether the image is protected or not. The copy-protection software is incorporated in applications which have a scan-print or a scan-store capability. A typical flow path of such a system is as follows:
a user places a photograph on a scanner platen; PA1 the user selects output print size desired; PA1 the system performs a low resolution scan; PA1 the system displays a digital image of the photograph; PA1 the user selects the print button; PA1 a software algorithm determines whether the image is copy restricted; PA1 if the image is not copy restricted, the system makes the print; or PA1 if the image is copy restricted, the user is prevented from making the print.
One problem with the prior art is that the software algorithm interprets the input image as a single photograph. If the user places multiple photographs on the scanner platen, some of which may be copy restrictive and some which are not copy restrictive, current systems cannot distinguish which photographs are copy restrictive and which are not, since the system only determines whether the entire input area is protected or not by sampling a portion of the input area. The reason for this is that it would be overly time consuming running the entire scanned image through the software algorithm to determine whether the entire image incorporates a microdot pattern indicating the photograph is copy restricted. Therefore, the system samples a portion of the scanned image, which may or may not be copy restrictive.
FIG. 1 shows a typical situation. A user placed several photographs 101-103 on a scanner at block 100. In this example, photographs 101 and 102 are not copy restricted and photograph 103 is copy restricted. The entire platen is then scanned. The software selects a section of the scanned image to check for the microdot pattern at block 110. In this scenario, the system looks for the protection pattern in a portion of the scanned image corresponding to photograph 101, which is not copy restrictive. The software algorithm searches the selected portion of the scanned image for the microdot pattern at block 120 and reports that the photographs scanned are not copy restrictive, although photograph 103 was copy restrictive.
Another problem with the current software copyright detection algorithms is that it contains only basic logic which distinguishes photographic data from platen data. More specifically, if the user scans a 5.times.7 inch area but the photograph was only 3.times.5 inches, the resultant image contains image data from the platen of the scanner. In addition, in cases where the user rotates the image, the scan of that image will undoubtedly contain platen data. The platen is typically white with a high code value, i.e., on a scale of 0-255, with black equal zero and white equal to 255, the value scanned area may be 240 or greater if it contains a significant portion of the platen. To distinguish platen information from photograph data, the current software algorithms compare the pixel values of the input scan area with a pre-calculated value such as 240. Since, the code values of the platen vary, there is a chance that the algorithm may mistake platen information for photograph information. Consequently, since platen information does not contain the copy protection pattern, it could cause the algorithm to report false results, e.g. the photograph was copy restrictive but the algorithm reports that it is not copy restrictive.
Prior art systems that incorporate software that allows the user to select one of several prints on a scanner platen for reprinting, make the system susceptible to allowing printing of copy restrictive photographs. For example, in one system, the user is allowed to select as input, a collage of photographs. The system performs a full platen scan. If some prints are copy restricted and some are not, the software algorithm may report that the area is not protected because it chose to look for the protection pattern in a part of the image that was not protected. Consequently, the user could successfully reprint a copy restrictive photograph. Alternatively, if the software algorithm had determined that the collage was copy restrictive, the user would have to try to determine which photograph was copy restricted, remove that photograph from the platen, and start the process over. This would be time consuming and decrease repeat business.
There are other ways to reproduce copy restrictive documents with prior art systems. If the user were knowledgeable about the operation of the system, she could rearrange the photographs on the platen. By doing so, the user may find the right arrangement of the photographs which would allow her to succeed in copying a copy restricted photograph.